The present invention relates to a position detection data generating method and apparatus for use in a position detection system which generates a first A.C. output signal having an electrical phase angle shifted in a phase-advancing or positive direction in accordance with a position of an object of detection and a second A.C. output signal having an electrical phase angle shifted in a phase-retreating or negative direction. More particularly, the present invention relates to a technique intended to improve detection performance with respect to dynamic characteristics of an object of detection (i.e., detecting characteristics when the object of detection is changing in position with time); for example, the present invention concerns a technique of detecting a rotational or linear position of an object of detection, such as a rotational position detector like a resolver or synchro or a linear position detector based on a position detecting principle similar to that of the rotational position detector.
Induction-type rotational position detector apparatus of the type which produces two-phase outputs (i.e., outputs of sine and cosine phases) in response to a single-phase exciting input are commonly known as xe2x80x9cresolversxe2x80x9d, and induction-type rotational position detector apparatus of the type which produces three-phase outputs (i.e., outputs of three phases shifted from each other by 120xc2x0) in response to a single-phase exciting input are commonly known as xe2x80x9csynchrosxe2x80x9d. In the resolvers of the most traditional type, a stator includes two-pole (sine and cosine poles) secondary windings that intersect each other at a 90xc2x0 mechanical angle, and a rotor includes a primary winding (the relationship between the primary and secondary windings may be reversed). The resolvers of this type are not satisfactory in that they need a brush to electrically contact the primary winding of the rotor. There have also been known brush-less resolvers that require no such brush; that is, these brush-less resolvers include, on the rotor side, a rotary transformer in place of the brush. The assignee of the instant application has recently developed an apparatus which, using a variable-reluctance-type detector having windings provided only on the stator (or the rotor), generates two-phase outputs (sine-phase and cosine-phase outputs) in response to a single-phase exciting input. The position detector apparatus which produce two-phase outputs (i.e., outputs of sine and cosine phases) in response to a single-phase exciting input as mentioned above have been proposed not only for the rotary position detection but also for the linear position detection.
The assignee of the instant application also proposed, in U.S. Pat. No. 5,710,509 (corresponding to Japanese Patent Laid-open Publication No. HEI-9-126809), a novel phase difference detection technique suitably applicable to the so-called resolver-type position detector apparatus producing two-phase outputs in response to a single-phase exciting input. This proposed phase difference detection technique gives a solution to the problem that A.C. signals induced in secondary windings would vary subtly in electric phase, in response to an ambient temperature change, to cause a detection error because the windings (coils) of the position detector apparatus vary in their impedance due to the ambient temperature change. The proposed phase difference detection technique generally comprises the following steps.
[Step 1] In response to a single-phase exciting input, the resolver-type position detector apparatus produces two A.C. output signals sin xcex8 sin xcfx89t and cos xcex8 sin xcfx89t having been amplitude-modulated by a sine function sin xcex8 and cosine function cos xcex8, respectively, corresponding to a phase angle xcex8 of a position of an object to be detected (hereinafter, also referred to as a xe2x80x9cposition-to-be-detectedxe2x80x9d). These A.C. output signals sin xcex8 sin xcfx89t and cos xcex8sin xcfx89t are processed electrically to generate a first A.C. output signal sin(xcfx89t+xcex8) having an electric phase angle (+xcex8) shifted in the phase-advancing or positive direction in accordance with the position-to-be-detected and a second A.C. output signal sin(xcfx89txe2x88x92xcex8) having an electric phase angle (xe2x88x92xcex8) shifted in the phase-retreating or negative direction in accordance with the position-to-be-detected. If a phase error component caused by a winding impedance variation due to an ambient temperature change is represented by xe2x80x9cxc2x1dxe2x80x9d, then the above-mentioned A.C. output signals can be expressed by sin(xcfx89txc2x1d+xcex8) and sin(xcfx89txc2x1dxe2x88x92xcex8), respectively.
[Step 2] Phase differences (xc2x1d+xcex8 and xc2x1dxe2x88x92xcex8) of the A.C. output signals from a predetermined reference phase (e.g., zero phase of sin xcfx89t) are detected, using a known digital phase difference measuring technique such as the xe2x80x9czero cross latchxe2x80x9d scheme, to thereby obtain respective phase detection data.
[Step 3] Arithmetic operation of xe2x80x9c{(xc2x1d+xcex8)+(xc2x1dxe2x88x92xcex8)}÷2=xc2x1dxe2x80x9d is performed using the thus-obtained phase detection data, to thereby calculate error data xc2x1d.
[Step 4] Error-free phase detection data xcex8 is obtained by subtracting the error data xc2x1d from one of the phase detection data (e.g., xc2x1d+xcex8).
When the position-to-be-detected varies over time, the phase angle xcex8 corresponding thereto would also vary over time, although no significant problem occurs when the position-to-be-detected is not moving. In such a case, the phase difference amount xcex8 of the A.C. output signals sin(xcfx89xc2x1d+xcex8) and sin(xcfx89txc2x1dxe2x88x92xcex8) would present, rather than a constant value, dynamic characteristics time-varying in correspondence with a moving speed of the object of detection. If the time-varying dynamic characteristics are represented collectively by xcex8(t), then the A.C. output signals can be expressed by sin{xcfx89txc2x1d+xcex8(t)} and sin{xcfx89txc2x1dxe2x88x92xcex8(t)}, respectively. Namely, by the well-known Doppler effect, the leading-phase A.C. output signal shifts to a higher frequency in accordance with the dynamic characteristics +xcex8(t), while the trailing-phase A.C. output signal shifts to a lower frequency in accordance with the dynamic characteristics xe2x88x92xcex8(t). Namely, with the dynamic characteristics, the cycles of the two A.C. output signals sequentially shift in the opposite directions per cycle of the reference signal sin xcfx89t, which would make it difficult to accurately calculate the phase variation error xc2x1d by only performing the arithmetic operation of Step 3 above.
Thus, to provide a good solution to such an inconvenience, the above-discussed prior phase difference detection technique is arranged to detect when there occurs a coincidence in zero cross between the two A.C. output signals sin{xcfx89txc2x1d+xcex8(t)} and sin{xcfx89txc2x1dxe2x88x92xcex8(t)}. More specifically, each time such a coincidence in zero cross between the two A.C. output signals is detected, the phase detection data of either one of the A.C. output signals sin{xcfx89txc2x1d+xcex8(t)} and sin{xcfx89txc2x1dxe2x88x92xcex8(t)} relative to the predetermined reference A.C. signal sin xcfx89t is held as the error data xc2x1d, and then the position detection data is modified at Step 4 above using the thus-held error data.
However, because the phase detection data can be obtained only when the zero crosses of the A.C. output signals sin(xcfx89t+xcex8) sin(xcfx89txe2x88x92xcex8) coincide with each other, the above-discussed prior phase difference detection technique faces the serious problem that the timewise detecting resolution of the phase detection data is limited to just one cyclic period of the A.C. signals and thus the response performance with respect to the dynamic characteristics (i.e., detecting characteristics when the position-to-be-detected is changing over time) is limited to a significant degree. Further, the response capability can be even further degraded because the detection of the error data xc2x1d taking the dynamic characteristics into account requires waiting for time points when a coincidence in zero cross occurs between the two A.C. output signals.
It is therefore an object of the present invention to provide a position detection data generating method and apparatus which achieve an improved response capability and detecting performance with respect to dynamic characteristics when applied to a position detecting system that produces a first A.C. output signal having an electric phase angle shifted in a positive direction in accordance with a position of an object of detection and a second A.C. output signal having an electric phase angle shifted in a negative direction in accordance with the position of the object of detection.
In order to accomplish the above-mentioned object, the present invention provides a position detection data generating method for use in a position detection system that produces a first A.C. output signal having an electric phase angle shifted in a positive direction in accordance with a position-to-be-detected and a second A.C. output signal having an electric phase angle shifted in a negative direction, which method comprises: a first step of generating first detection data by detecting a phase difference of the first A.C. output signal from a predetermined reference phase and generating second detection data by detecting a phase difference of the second A.C. output signal from the predetermined reference phase; a second step of providing a first predicted value on the basis of at least two samples of the first detection data and providing a second predicted value on the basis of at least two samples of the second detection data; a third step of providing at least one standard predicted value on the basis of the first and second predicted values; a fourth step of performing interpolation on the first detection data and the second detection data, sequentially with passage of time, using the standard predicted value, to thereby provide first interpolated detection data and second interpolated detection data; and a fifth step of, on the basis of the first and second interpolated detection data, outputting position detection data corresponding to the position-to-be-detected.
In one preferred implementation, the above-mentioned fifth step includes a step of obtaining error data contained in the first and second detection data by performing an arithmetic operation between the first and second interpolated detection data provided by the fourth step, and a step of providing interpolated position detection data indicative of the position-to-be-detected by performing an arithmetic operation to remove the error data from one of the first and second interpolated detection data.
The present invention can improve its response performance with respect to dynamic characteristics (detecting characteristics when the position-to-be-detected is changing over time) by generating the first and second interpolated detection data, densely at close time intervals, through the predictive interpolation operation. Thus, the timewise density or precision of the first and second interpolated detection data can be increased significantly, which allows the error data to be calculated whenever necessary by the fifth step and which therefore can eliminate the need to wait for a time point where a coincidence in zero cross occurs between the two A.C. output signals as in the conventionally-known techniques; therefore, the present invention achieves an improved response capability or responsivity. Further, with the arrangement that at least one standard predicted value is determined by the third step on the basis of the first and second predicted values, the present invention can appropriately correct an error that is likely to occur in the interpolating arithmetic operation due to a possible difference in linearity of frequency transition (cyclic period transition) caused by the Doppler effect between the signals phase-shifted in the positive and negative directions. As a consequence, the present invention can perform the interpolating arithmetic operation with increased accuracy.
The present invention also provides a position detection data generating method for use in a position detection system that produces a first A.C. output signal having an electric phase angle shifted in a positive direction in accordance with a position-to-be-detected and a second A.C. output signal having an electric phase angle shifted in a negative direction, which method comprises: a first step of generating first detection data by detecting a phase difference of the first A.C. output signal from a predetermined reference phase and generating second detection data by detecting a phase difference of the second A.C. output signal from the predetermined reference phase; a second step of providing first interpolated output data by performing predictive interpolation, using at least two samples of the first detection data, sequentially with passage of time and at time intervals of interpolation steps each shorter than an A.C. period of the reference phase; a third step of providing second interpolated output data by performing predictive interpolation, using at least two samples of the second detection data, at the time intervals of interpolation steps; a fourth step of obtaining error data contained in the first and second detection data by performing an arithmetic operation between the first and second interpolated output data provided by the second and third steps; and a fifth step of providing interpolated position detection data indicative of the position-to-be-detected by performing an arithmetic operation to remove the error data from one of the first and second interpolated output data. With this method too, the response performance with respect to dynamic characteristics can be significantly improved by generating the first and second interpolated detection data, densely at close time intervals, through the predictive interpolation. Thus, the timewise density or precision of the first and second interpolated detection data can be increased, which allows the error data to be calculated whenever necessary by the fourth step and which therefore can eliminate the need to wait for a time point where a coincidence in zero cross occurs between the two A.C. output signals as in the conventionally-known techniques; as a consequence, the present invention achieves an improved response capability.
Further, the present invention provides a position detection data generating method for use in a position detection system which produces a first A.C. output signal having an electric phase angle shifted in a positive direction in accordance with a position-to-be-detected and a second A.C. output signal having an electric phase angle shifted in a negative direction, which comprises: a first step of generating first detection data by detecting a phase difference of the first A.C. output signal from a predetermined reference phase and generating second detection data by detecting a phase difference of the second A.C. output signal from the predetermined reference phase; a second step of providing interpolation data for performing predictive interpolation, using at least two samples of the first detection data and at least two samples of the second detection data, sequentially with passage of time and at time intervals of interpolation steps each shorter than an A.C. period of the reference phase; a third step of obtaining error data contained in the first and second detection data; and a fourth step of, for at least one of the first and second detection data, performing an arithmetic operation using the interpolation data and error data, to thereby provide interpolated position detection data corresponding to the one of the first and second detection data from which the error data has been removed and which has been subjected to predictive interpolation. With this method too, the response performance with respect to dynamic characteristics can be significantly improved by generating the first and second interpolated detection data, densely at close time intervals, through the predictive interpolation. Thus, the timewise density or precision of the first and second interpolated detection data can be increased, which allows the error data to be calculated whenever necessary by the third step and which therefore can eliminate the need to wait for a time point where a coincidence in zero cross occurs between the two A.C. output signals as in the conventionally-known techniques; as a consequence, the present invention achieves an improved response capability.
The present invention may be constructed and implemented not only as the method invention as set out above but also as a system or apparatus invention. The present invention may also be practiced as a program for execution by a processor such as a computer or DSP, or a storage medium storing such a program.